Intracorporeal devices are devices suitable for introduction into a patient's body, for example, into a body lumen of a patient. Many clinical procedures require the insertion of wires, tubes, probes or other objects into a body lumen of a patient. For example, guidewires and catheters may be used for gaining access to the coronary vasculature, as in an angiogram or in angioplasty. A guidewire is a thin, flexible device used to provide a guiding rail to a desired location within the vasculature (or other body cavity) of a patient. A balloon catheter is a device with an interior lumen with at least a portion of the catheter being able to expand. In coronary angioplasty, a balloon catheter, guided by a guidewire, is positioned within a partially-occluded coronary artery where its balloon portion is expanded in order to press against and enlarge the lumen of a blood vessel in which it is situated. Alternatively, endoscopy requires the introduction of an endoscope into the lumen of a patient, as may be done during a colonoscopy.
The ability to decide where to locate a catheter during a clinical procedure can be improved by providing interior images of the body lumen, such as the blood vessels during angioplasty or the colon during colonoscopy. It is often critical to the success of an angioplasty procedure that a balloon catheter be properly located within a blood vessel. Thus; imaging by guidewire, catheter, or other such device can be of great importance to the success of the procedure.
Imaging endoscopes, guidewires and catheters have been described, as in U.S. Pat. Nos. 5,321,501 and 5,459,570 to Swanson et al., and U.S. Pat. No. 6,134,003 to Tearney et al. Catheters adapted for optical imaging using non-visible light may be useful as well, as disclosed in U.S. Pat. No. 5,935,075 to Cassells et al. Such imaging devices typically use an optical fiber to carry light. All patents, supra and infra, are hereby incorporated by reference in their entirety.
It is often advantageous to have a window in an imaging catheter, imaging guidewire, endoscope, or other imaging probe to allow optical access between the exterior of the device and the optical fiber or light path within the device. U.S. Pat. No. 6,134,003 to Tearney et al. discloses a rigid plastic clear window, or using three or more metal or plastic metering rods to connect two parts of a guidewire across a window. However, the choice of material and the method of construction of the window is critical to the success of the device. A window made of brittle material may break and shatter if it fails, leading to the dispersion of broken window shards within a body lumen if such failure occurs during a clinical procedure. Such materials are thus unacceptable in devices designed for use within a body lumen. A non-brittle, plastic material does not have the disadvantages of a brittle window material.
However, a suitable connection between the window material and other components of an intracorporeal imaging device is required. For use in an intracorporeal imaging device such as a guidewire, catheter, or endoscope, the window must be attached to proximal and distal portions of the intracorporeal imaging device.
Conventional techniques for forming and attaching windows have been found to be difficult and unsuccessful. Use of rods to connect two parts of a guidewire or other intracorporeal imaging device across a window blocks visual access and interferes with the imaging function of a window. The extremely small dimensions of the window components makes conventional molding, extrusion molding, injection molding and insert molding processes difficult and costly to use in making a window for these intracorporeal devices, and such methods only provide a low likelihood of success.
For example, the small outer diameter of a guidewire makes it extremely difficult to use conventional methods to successfully press fit an extruded window over the formed guidewire mating ends. Conventional attempts to expand or drill out the inner diameter of the window tubing to obtain a fit present problems with alignment, obtaining tooling and maintaining low enough tolerances to make a good bond of either desired type. Further, if one were to use conventional techniques and to expand the extruded window to allow a fit over the ends of the guidewire, some window material would assume a larger than desired outer diameter, which would have to be cleanly removed by some other operation. Additionally, the tolerances associated with extrusion (typically +/−0.001″) would require that the average cross-sectional area of the window wall be significantly lower than the maximum cross-section possible within its dimensional constraints, so that, with prior art methods, the strength and utility of the window could be impaired.
Conventional methods for bonding the ends of the window with an adhesive so as to mate appropriately with the proximal and distal portions of a guidewire or catheter suffer from similar disadvantages as other conventional methods. Conventional molding processes force a melted plastic into a mold cavity where it rapidly cools. In order to form a tubular window a mold pin must be placed inside the mold to leave a hollow interior. However, with such conventional techniques, while forcing melted plastic into a mold, at least a portion of the melted plastic would cool significantly while flowing into the mold. Conventional techniques would then require that the plastic be forced very rapidly into the cavity under high pressures to fill the cavity before cooling in an attempt to avoid this problem. However, such rapid, high pressure flow would damage or warp the mold pin forming the inner diameter of the window. This is due to the length of the window inner diameter that is required to ensure that the fiber optic assembly can be reliably aligned such that the light exits the window in all bend, temperature and assembly conditions.
Attempting to balance the molding forces by having more than one plastic entrance into the mold requires a more complex and expensive mold. This method suffers from disadvantages due to the low volume of plastic in the window, and the uncertainty involved in timing the plastic flow's entry into the cavity. Additionally, molds and equipment of this type are very expensive.
Accordingly, there is need in the art for methods for forming a window for an imaging guidewire, catheter or endoscope.